In the consumer electronics and computer industries, transmission of audio signals from a host player to remote device speakers has generally been accomplished over an analog wired interface, known commonly as speaker wires. With the advent of digital audio content, the desire to maintain the pristine digital audio signal as far as possible along the audio signal chain has motivated designers to pursue digital interfaces to replace unsightly, signal-loss-prone analog speaker wires.
Digital audio data can be transferred between devices utilizing physically connected (wired or optical-link) interfaces or wireless interfaces. Interfaces such as Sony/Philips Digital Interface Format (“SPDIF”) carry 2-channel uncompressed audio data or multi-channel highly-compressed audio data, and utilize a wired or optical medium which is expected to yield no data errors in transmission. These interfaces are generally limited to short cable lengths to maintain error-free transmission. Because these links are expected to be error-free, the audio data which they carry is encoded with simple error detection or no error detection at all, and no error correction. As a result of these limitations, SPDIF interfaces are not well-suited to replace analog speaker wires.
To enable the transmission of multi-channel uncompressed audio, and lossless, or minimally-lossy multi-channel compressed audio, the need for higher-bandwidth interfaces becomes necessary. High-speed wired serial links, such as HDMI and USB, have bandwidth capabilities to carry higher audio data rates, but these interfaces are non-error-free, with packet error rates of 10−9 for minimal compliance to their specifications. With this admission of even highly occasional errors, the possibility of audio interruption (periods of time with no audible sound) or audio disturbances (audible pops and cracks) is introduced. USB has no error correction encoding for audio, and therefore, when the link fails, audio is either interrupted or disturbed, making analog speaker wires preferable to most. Also, a topology allowing multiple USB speakers, each of which is digitally interconnected, requires a USB host to USB hub with enough ports to accommodate the number of USB speakers in the system, and a USB cable between each speaker and the hub. Because audio is often played alongside “lip-synched” video, concerns about audio latency and speaker synchronization after going through the multiple levels of the above topology also becomes a concern. HDMI concurrently carries both digital video and audio, and thereby can avoid lip-sync concerns, has enough bandwidth, and employs error correction methods for audio to enable systems that carry high quality, multi-channel audio that does not introduce audio interruption or disturbances. However, to enable HDMI digital audio transmission to remote speakers requires a topology somewhat similar to that described above for USB. HDMI source to speaker systems would require a separate HDMI transmitter for each speaker's HDMI receiver, with an HDMI cable between each pair. This quickly becomes quite costly for systems which support 6 or 8 speakers. To cover distances that would be required for surround speakers, HDMI cables generally need to be thicker, making them cumbersome and costly, and HDMI source to speakers systems quickly become less compelling compared to analog speaker wires.
To solve the above problems, wireless interconnects, or “invisible” wired interconnects, such as HomePlug power line communications, become desirable. Wireless or HomePlug systems, however, provide lower bandwidth than HDMI, and have higher, and more variable data error rates than HDMI. But, they have the large advantage of removing the visible audio transmission wires while maintaining pristine digital audio.
Many wireless media could be used for audio, such as infra-red (IR) and consumer radio frequency (RF) systems, but most suffer from limited bandwidth, insurmountable interference, restrictive line-of-sight, and/or lip-sync-compromising latency requirements.
FIG. 1 shows an example of a conventional prior art audio video system, comprised of a source (HDMI DVD player 8) connected via an HDMI cable to an audio-video receiver (HDMI AV Rx 9) connected via an HDMI cable to a display (HDMI TV 22). The HDMI AV Rx 9 is also connected via analog speaker wires to a set of 6 speakers (1-6), each connected point-to-point from the HDMI AV Rx 9. Speakers in FIG. 1 are identified as follows: Front Left (FL) 1, Front Right (FR) 2, Center (C) 5, Surround Left (SL) 3, Surround Right (SR) 4, and Low Frequency Effect (LFE) 6, also commonly referred to as a “subwoofer.” This conventional system contains components which can maintain pristine digital audio and video from source to display through HDMI interconnects, but from the AV Rx 9 to the speakers 1-6, the interconnect is still analog, via conventional speaker wires. With such a system containing 6 individual speakers, and other, more advanced systems which support up to 8 speakers or more, the speaker wire interconnections not only suffer from analog signal loss, but they can cause quite an eyesore or minimally a wire-hiding challenge, especially for those speakers intended to be located far from the source, such as the Surround Left (SL) 3 and Surround Right (SR) 4 speakers.